<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.25.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>995</ContextCount>
  <ElementCount>737</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>166</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>11</UnitCount>
  <MyReports>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0000001 - Document - Cover</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/Cover</Role>
      <ShortName>Cover</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>0000002 - Document - Audit Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/AuditInformation</Role>
      <ShortName>Audit Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>9952151 - Statement - CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/CONSOLIDATEDSTATEMENTSOFFINANCIALCONDITION</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>9952152 - Statement - CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/CONSOLIDATEDSTATEMENTSOFFINANCIALCONDITIONParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>9952153 - Statement - CONSOLIDATED STATEMENTS OF INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/CONSOLIDATEDSTATEMENTSOFINCOME</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>9952154 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>9952155 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMEParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>9952156 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITY</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>9952157 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITYParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>9952158 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWS</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>9952159 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWSParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>9952160 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/SummaryofSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>9952161 - Disclosure - Recently Adopted Accounting Standards</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/RecentlyAdoptedAccountingStandards</Role>
      <ShortName>Recently Adopted Accounting Standards</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>9952162 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/Leases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>9952163 - Disclosure - Marketable Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/MarketableSecurities</Role>
      <ShortName>Marketable Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>9952164 - Disclosure - Loans Receivable</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivable</Role>
      <ShortName>Loans Receivable</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>9952165 - Disclosure - Accrued Interest Receivable</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/AccruedInterestReceivable</Role>
      <ShortName>Accrued Interest Receivable</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>9952166 - Disclosure - FHLB Stock</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/FHLBStock</Role>
      <ShortName>FHLB Stock</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>9952167 - Disclosure - Premises and Equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/PremisesandEquipment</Role>
      <ShortName>Premises and Equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>9952168 - Disclosure - Goodwill and Other Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/GoodwillandOtherIntangibleAssets</Role>
      <ShortName>Goodwill and Other Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>9952169 - Disclosure - Deposits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/Deposits</Role>
      <ShortName>Deposits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>9952170 - Disclosure - Borrowed Funds</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/BorrowedFunds</Role>
      <ShortName>Borrowed Funds</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>9952171 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>9952172 - Disclosure - Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ShareholdersEquity</Role>
      <ShortName>Shareholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>9952173 - Disclosure - Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EarningsPerShare</Role>
      <ShortName>Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>9952174 - Disclosure - Employee Benefit Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlans</Role>
      <ShortName>Employee Benefit Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>9952175 - Disclosure - Disclosures About Fair Value of Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DisclosuresAboutFairValueofFinancialInstruments</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>9952176 - Disclosure - Regulatory Capital Requirements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/RegulatoryCapitalRequirements</Role>
      <ShortName>Regulatory Capital Requirements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>9952177 - Disclosure - Contingent Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ContingentLiabilities</Role>
      <ShortName>Contingent Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>9952178 - Disclosure - Legal Proceedings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LegalProceedings</Role>
      <ShortName>Legal Proceedings</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>9952179 - Disclosure - Components of Accumulated Other Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ComponentsofAccumulatedOtherComprehensiveIncome</Role>
      <ShortName>Components of Accumulated Other Comprehensive Income</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>9952180 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/SegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>9952181 - Disclosure - Parent Company Only Financial Statements - Condensed</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ParentCompanyOnlyFinancialStatementsCondensed</Role>
      <ShortName>Parent Company Only Financial Statements - Condensed</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>9952182 - Disclosure - Derivative Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DerivativeFinancialInstruments</Role>
      <ShortName>Derivative Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>995410 - Disclosure - Pay vs Performance Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/PvpDisclosure</Role>
      <ShortName>Pay vs Performance Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>995447 - Disclosure - Insider Trading Policies and Procedures</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingPoliciesProc</Role>
      <ShortName>Insider Trading Policies and Procedures</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>995550 - Disclosure - Cybersecurity Risk Management and Strategy Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/cyd/role/CybersecurityRiskManagementAndStrategyDisclosure</Role>
      <ShortName>Cybersecurity Risk Management and Strategy Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>9955511 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/SummaryofSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/SummaryofSignificantAccountingPolicies</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>9955512 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/Leases</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>9955513 - Disclosure - Marketable Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/MarketableSecuritiesTables</Role>
      <ShortName>Marketable Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/MarketableSecurities</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>9955514 - Disclosure - Loans Receivable (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableTables</Role>
      <ShortName>Loans Receivable (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/LoansReceivable</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>9955515 - Disclosure - Accrued Interest Receivable (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/AccruedInterestReceivableTables</Role>
      <ShortName>Accrued Interest Receivable (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/AccruedInterestReceivable</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>9955516 - Disclosure - Premises and Equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/PremisesandEquipmentTables</Role>
      <ShortName>Premises and Equipment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/PremisesandEquipment</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>9955517 - Disclosure - Goodwill and Other Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/GoodwillandOtherIntangibleAssetsTables</Role>
      <ShortName>Goodwill and Other Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/GoodwillandOtherIntangibleAssets</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>9955518 - Disclosure - Deposits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DepositsTables</Role>
      <ShortName>Deposits (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/Deposits</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>9955519 - Disclosure - Borrowed Funds (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/BorrowedFundsTables</Role>
      <ShortName>Borrowed Funds (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/BorrowedFunds</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>9955520 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/IncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/IncomeTaxes</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>9955521 - Disclosure - Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EarningsPerShareTables</Role>
      <ShortName>Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/EarningsPerShare</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>9955522 - Disclosure - Employee Benefit Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlansTables</Role>
      <ShortName>Employee Benefit Plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlans</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>9955523 - Disclosure - Disclosures About Fair Value of Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DisclosuresAboutFairValueofFinancialInstrumentsTables</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/DisclosuresAboutFairValueofFinancialInstruments</ParentRole>
      <Position>51</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>9955524 - Disclosure - Regulatory Capital Requirements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/RegulatoryCapitalRequirementsTables</Role>
      <ShortName>Regulatory Capital Requirements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/RegulatoryCapitalRequirements</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>9955525 - Disclosure - Components of Accumulated Other Comprehensive Income (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ComponentsofAccumulatedOtherComprehensiveIncomeTables</Role>
      <ShortName>Components of Accumulated Other Comprehensive Income (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/ComponentsofAccumulatedOtherComprehensiveIncome</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>9955526 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/SegmentInformationTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/SegmentInformation</ParentRole>
      <Position>54</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>9955527 - Disclosure - Parent Company Only Financial Statements - Condensed (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ParentCompanyOnlyFinancialStatementsCondensedTables</Role>
      <ShortName>Parent Company Only Financial Statements - Condensed (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/ParentCompanyOnlyFinancialStatementsCondensed</ParentRole>
      <Position>55</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>9955528 - Disclosure - Derivative Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DerivativeFinancialInstrumentsTables</Role>
      <ShortName>Derivative Financial Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/DerivativeFinancialInstruments</ParentRole>
      <Position>56</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>9955529 - Disclosure - Summary of Significant Accounting Policies - Loans Receivable and Allowance for Loan Losses and Other Narrative Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/SummaryofSignificantAccountingPoliciesLoansReceivableandAllowanceforLoanLossesandOtherNarrativeInformationDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Loans Receivable and Allowance for Loan Losses and Other Narrative Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>9955530 - Disclosure - Summary of Significant Accounting Policies - Premises and Equipment and Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/SummaryofSignificantAccountingPoliciesPremisesandEquipmentandGoodwillDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Premises and Equipment and Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>9955531 - Disclosure - Summary of Significant Accounting Policies - Pension Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/SummaryofSignificantAccountingPoliciesPensionPlansDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Pension Plans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>9955532 - Disclosure - Summary of Significant Accounting Policies - Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/SummaryofSignificantAccountingPoliciesLeasesDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/SummaryofSignificantAccountingPoliciesPolicies</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>9955533 - Disclosure - Leases - Schedule of Lease Cost (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LeasesScheduleofLeaseCostDetails</Role>
      <ShortName>Leases - Schedule of Lease Cost (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>9955534 - Disclosure - Leases - Schedule of Lease Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LeasesScheduleofLeaseAssetsandLiabilitiesDetails</Role>
      <ShortName>Leases - Schedule of Lease Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>9955535 - Disclosure - Leases - Schedule of Supplemental Cash Flow Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LeasesScheduleofSupplementalCashFlowInformationDetails</Role>
      <ShortName>Leases - Schedule of Supplemental Cash Flow Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>9955536 - Disclosure - Leases - Schedule of Lease Maturities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LeasesScheduleofLeaseMaturitiesDetails</Role>
      <ShortName>Leases - Schedule of Lease Maturities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>9955537 - Disclosure - Leases - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LeasesNarrativeDetails</Role>
      <ShortName>Leases - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>9955538 - Disclosure - Marketable Securities - Available-for-sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/MarketableSecuritiesAvailableforsaleDetails</Role>
      <ShortName>Marketable Securities - Available-for-sale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>9955539 - Disclosure - Marketable Securities - Held-to-maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/MarketableSecuritiesHeldtomaturityDetails</Role>
      <ShortName>Marketable Securities - Held-to-maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>9955540 - Disclosure - Marketable Securities - Available-for-sale, by Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/MarketableSecuritiesAvailableforsalebyContractualMaturityDetails</Role>
      <ShortName>Marketable Securities - Available-for-sale, by Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>9955541 - Disclosure - Marketable Securities - Held-to-maturity, by Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/MarketableSecuritiesHeldtomaturitybyContractualMaturityDetails</Role>
      <ShortName>Marketable Securities - Held-to-maturity, by Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>9955542 - Disclosure - Marketable Securities - Issuers and the Carrying Values of Mortgage-backed Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/MarketableSecuritiesIssuersandtheCarryingValuesofMortgagebackedSecuritiesDetails</Role>
      <ShortName>Marketable Securities - Issuers and the Carrying Values of Mortgage-backed Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>9955543 - Disclosure - Marketable Securities - Fair Value and Gross Unrealized Losses on Marketable Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/MarketableSecuritiesFairValueandGrossUnrealizedLossesonMarketableSecuritiesDetails</Role>
      <ShortName>Marketable Securities - Fair Value and Gross Unrealized Losses on Marketable Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>9955544 - Disclosure - Marketable Securities - Held-to-maturity Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/MarketableSecuritiesHeldtomaturitySecuritiesDetails</Role>
      <ShortName>Marketable Securities - Held-to-maturity Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>9955545 - Disclosure - Loans Receivable - Schedule of Originated and Acquired Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableScheduleofOriginatedandAcquiredLoansDetails</Role>
      <ShortName>Loans Receivable - Schedule of Originated and Acquired Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>9955546 - Disclosure - Loans Receivable - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableNarrativeDetails</Role>
      <ShortName>Loans Receivable - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>9955547 - Disclosure - Loans Receivable - Changes in the Allowance for Losses on Loans Receivable (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableChangesintheAllowanceforLossesonLoansReceivableDetails</Role>
      <ShortName>Loans Receivable - Changes in the Allowance for Losses on Loans Receivable (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>9955548 - Disclosure - Loans Receivable - Loan Portfolio by Portfolio Segment and by Class of Financing Receivable (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableLoanPortfoliobyPortfolioSegmentandbyClassofFinancingReceivableDetails</Role>
      <ShortName>Loans Receivable - Loan Portfolio by Portfolio Segment and by Class of Financing Receivable (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>9955549 - Disclosure - Loans Receivable - Composition of Impaired Loans by Portfolio Segment and Class of Financing Receivable (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableCompositionofImpairedLoansbyPortfolioSegmentandClassofFinancingReceivableDetails</Role>
      <ShortName>Loans Receivable - Composition of Impaired Loans by Portfolio Segment and Class of Financing Receivable (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>9955550 - Disclosure - Loans Receivable - Amortized Cost Basis of Loans Modified (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableAmortizedCostBasisofLoansModifiedDetails</Role>
      <ShortName>Loans Receivable - Amortized Cost Basis of Loans Modified (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>9955551 - Disclosure - Loans Receivable - Financing Receivable Weighted Average Modified Period (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableFinancingReceivableWeightedAverageModifiedPeriodDetails</Role>
      <ShortName>Loans Receivable - Financing Receivable Weighted Average Modified Period (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>9955552 - Disclosure - Loans Receivable - Performance of Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivablePerformanceofLoansDetails</Role>
      <ShortName>Loans Receivable - Performance of Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>9955553 - Disclosure - Loans Receivable - Schedule of Amortized Cost Basis of Financing Receivables that had a Payment Default (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableScheduleofAmortizedCostBasisofFinancingReceivablesthathadaPaymentDefaultDetails</Role>
      <ShortName>Loans Receivable - Schedule of Amortized Cost Basis of Financing Receivables that had a Payment Default (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>9955554 - Disclosure - Loans Receivable - Loan Delinquencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableLoanDelinquenciesDetails</Role>
      <ShortName>Loans Receivable - Loan Delinquencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>9955555 - Disclosure - Loans Receivable - Credit Quality Indicators (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableCreditQualityIndicatorsDetails</Role>
      <ShortName>Loans Receivable - Credit Quality Indicators (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>9955556 - Disclosure - Loans Receivable - Off-Balance Sheet Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableOffBalanceSheetFinancialInstrumentsDetails</Role>
      <ShortName>Loans Receivable - Off-Balance Sheet Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>9955557 - Disclosure - Loans Receivable - Mortgage Servicing Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/LoansReceivableMortgageServicingAssetsDetails</Role>
      <ShortName>Loans Receivable - Mortgage Servicing Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>9955558 - Disclosure - Accrued Interest Receivable (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/AccruedInterestReceivableDetails</Role>
      <ShortName>Accrued Interest Receivable (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/AccruedInterestReceivableTables</ParentRole>
      <Position>86</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>9955559 - Disclosure - FHLB Stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/FHLBStockDetails</Role>
      <ShortName>FHLB Stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/FHLBStock</ParentRole>
      <Position>87</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>9955560 - Disclosure - Premises and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/PremisesandEquipmentDetails</Role>
      <ShortName>Premises and Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/PremisesandEquipmentTables</ParentRole>
      <Position>88</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>9955561 - Disclosure - Goodwill and Other Intangible Assets - Schedule of Other Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/GoodwillandOtherIntangibleAssetsScheduleofOtherIntangibleAssetsDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Schedule of Other Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>89</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>9955562 - Disclosure - Goodwill and Other Intangible Assets - Changes in the Carrying Amount of Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/GoodwillandOtherIntangibleAssetsChangesintheCarryingAmountofGoodwillDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Changes in the Carrying Amount of Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>90</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>9955563 - Disclosure - Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DepositsDetails</Role>
      <ShortName>Deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/DepositsTables</ParentRole>
      <Position>91</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>9955564 - Disclosure - Borrowed Funds - Schedule of Borrowed Funds (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/BorrowedFundsScheduleofBorrowedFundsDetails</Role>
      <ShortName>Borrowed Funds - Schedule of Borrowed Funds (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>92</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>9955565 - Disclosure - Borrowed Funds - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/BorrowedFundsNarrativeDetails</Role>
      <ShortName>Borrowed Funds - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>93</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>9955566 - Disclosure - Borrowed Funds - Schedule of Capital Debt Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/BorrowedFundsScheduleofCapitalDebtSecuritiesDetails</Role>
      <ShortName>Borrowed Funds - Schedule of Capital Debt Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>94</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>9955567 - Disclosure - Income Taxes - Schedule of Income Tax (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/IncomeTaxesScheduleofIncomeTaxDetails</Role>
      <ShortName>Income Taxes - Schedule of Income Tax (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>95</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>9955568 - Disclosure - Income Taxes - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/IncomeTaxesNarrativeDetails</Role>
      <ShortName>Income Taxes - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>96</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>9955569 - Disclosure - Income Taxes - Schedule of Unrecognized Tax Benefits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/IncomeTaxesScheduleofUnrecognizedTaxBenefitsDetails</Role>
      <ShortName>Income Taxes - Schedule of Unrecognized Tax Benefits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>97</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>9955570 - Disclosure - Shareholders' Equity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ShareholdersEquityDetails</Role>
      <ShortName>Shareholders' Equity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/ShareholdersEquity</ParentRole>
      <Position>98</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>9955571 - Disclosure - Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EarningsPerShareComputationofBasicandDilutedEarningsPerShareDetails</Role>
      <ShortName>Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>99</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R100.htm</HtmlFileName>
      <LongName>9955572 - Disclosure - Employee Benefit Plans - Pension Plans, Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlansPensionPlansNarrativeDetails</Role>
      <ShortName>Employee Benefit Plans - Pension Plans, Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>100</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R101.htm</HtmlFileName>
      <LongName>9955573 - Disclosure - Employee Benefit Plans - Pension Plans - Components of Net Periodic Pension Cost and Other Amounts Recognized In OCI (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlansPensionPlansComponentsofNetPeriodicPensionCostandOtherAmountsRecognizedInOCIDetails</Role>
      <ShortName>Employee Benefit Plans - Pension Plans - Components of Net Periodic Pension Cost and Other Amounts Recognized In OCI (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>101</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R102.htm</HtmlFileName>
      <LongName>9955574 - Disclosure - Employee Benefit Plans - Defined Benefit Pension Plans' Funded Status (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlansDefinedBenefitPensionPlansFundedStatusDetails</Role>
      <ShortName>Employee Benefit Plans - Defined Benefit Pension Plans' Funded Status (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>102</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R103.htm</HtmlFileName>
      <LongName>9955575 - Disclosure - Employee Benefit Plans - Defined Benefit Plans Certain Information and Weighted Average Asset Allocation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlansDefinedBenefitPlansCertainInformationandWeightedAverageAssetAllocationDetails</Role>
      <ShortName>Employee Benefit Plans - Defined Benefit Plans Certain Information and Weighted Average Asset Allocation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>103</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R104.htm</HtmlFileName>
      <LongName>9955576 - Disclosure - Employee Benefit Plans - Pension Plan Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlansPensionPlanAssetsDetails</Role>
      <ShortName>Employee Benefit Plans - Pension Plan Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>104</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R105.htm</HtmlFileName>
      <LongName>9955577 - Disclosure - Employee Benefit Plans - Stock-based Compensation, Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlansStockbasedCompensationNarrativeDetails</Role>
      <ShortName>Employee Benefit Plans - Stock-based Compensation, Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>105</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R106.htm</HtmlFileName>
      <LongName>9955578 - Disclosure - Employee Benefit Plans - Schedule of Share-Based, Granted (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlansScheduleofShareBasedGrantedDetails</Role>
      <ShortName>Employee Benefit Plans - Schedule of Share-Based, Granted (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>106</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R107.htm</HtmlFileName>
      <LongName>9955579 - Disclosure - Employee Benefit Plans - Stock Option Plans, Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlansStockOptionPlansNarrativeDetails</Role>
      <ShortName>Employee Benefit Plans - Stock Option Plans, Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>107</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R108.htm</HtmlFileName>
      <LongName>9955580 - Disclosure - Employee Benefit Plans - Share-Based Awards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlansShareBasedAwardsDetails</Role>
      <ShortName>Employee Benefit Plans - Share-Based Awards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>108</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R109.htm</HtmlFileName>
      <LongName>9955581 - Disclosure - Employee Benefit Plans - Number of Options Outstanding and Exercisable and Weighted Average Remaining Life of All Option Grants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/EmployeeBenefitPlansNumberofOptionsOutstandingandExercisableandWeightedAverageRemainingLifeofAllOptionGrantsDetails</Role>
      <ShortName>Employee Benefit Plans - Number of Options Outstanding and Exercisable and Weighted Average Remaining Life of All Option Grants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>109</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R110.htm</HtmlFileName>
      <LongName>9955582 - Disclosure - Disclosures About Fair Value of Financial Instruments - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DisclosuresAboutFairValueofFinancialInstrumentsNarrativeDetails</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/DisclosuresAboutFairValueofFinancialInstrumentsTables</ParentRole>
      <Position>110</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R111.htm</HtmlFileName>
      <LongName>9955583 - Disclosure - Disclosures About Fair Value of Financial Instruments - Carrying Amount and Estimated Fair Value of Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DisclosuresAboutFairValueofFinancialInstrumentsCarryingAmountandEstimatedFairValueofFinancialInstrumentsDetails</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments - Carrying Amount and Estimated Fair Value of Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>111</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R112.htm</HtmlFileName>
      <LongName>9955584 - Disclosure - Disclosures About Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DisclosuresAboutFairValueofFinancialInstrumentsAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisDetails</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>112</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R113.htm</HtmlFileName>
      <LongName>9955585 - Disclosure - Disclosures About Fair Value of Financial Instruments - Reconciliation of all Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DisclosuresAboutFairValueofFinancialInstrumentsReconciliationofallAssetsandLiabilitiesMeasuredatFairValueonaRecurringBasisUsingSignificantUnobservableInputsLevel3Details</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments - Reconciliation of all Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Level 3) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>113</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R114.htm</HtmlFileName>
      <LongName>9955586 - Disclosure - Disclosures About Fair Value of Financial Instruments - Nonrecurring Assets that had Fair Market Values Below the Carrying Amount (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DisclosuresAboutFairValueofFinancialInstrumentsNonrecurringAssetsthathadFairMarketValuesBelowtheCarryingAmountDetails</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments - Nonrecurring Assets that had Fair Market Values Below the Carrying Amount (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>114</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R115.htm</HtmlFileName>
      <LongName>9955587 - Disclosure - Disclosures About Fair Value of Financial Instruments - Additional Quantitative Information, Assets Measured at Fair Value, Recurring and Nonrecurring Basis, Level 3 Input (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DisclosuresAboutFairValueofFinancialInstrumentsAdditionalQuantitativeInformationAssetsMeasuredatFairValueRecurringandNonrecurringBasisLevel3InputDetails</Role>
      <ShortName>Disclosures About Fair Value of Financial Instruments - Additional Quantitative Information, Assets Measured at Fair Value, Recurring and Nonrecurring Basis, Level 3 Input (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>115</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R116.htm</HtmlFileName>
      <LongName>9955588 - Disclosure - Regulatory Capital Requirements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/RegulatoryCapitalRequirementsDetails</Role>
      <ShortName>Regulatory Capital Requirements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/RegulatoryCapitalRequirementsTables</ParentRole>
      <Position>116</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R117.htm</HtmlFileName>
      <LongName>9955589 - Disclosure - Components of Accumulated Other Comprehensive Income - Schedule of Components (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ComponentsofAccumulatedOtherComprehensiveIncomeScheduleofComponentsDetails</Role>
      <ShortName>Components of Accumulated Other Comprehensive Income - Schedule of Components (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>117</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R118.htm</HtmlFileName>
      <LongName>9955590 - Disclosure - Components of Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income by Component (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ComponentsofAccumulatedOtherComprehensiveIncomeChangesinAccumulatedOtherComprehensiveIncomebyComponentDetails</Role>
      <ShortName>Components of Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income by Component (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>118</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R119.htm</HtmlFileName>
      <LongName>9955591 - Disclosure - Segment Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/SegmentInformationDetails</Role>
      <ShortName>Segment Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.northwestsavingsbank.com/role/SegmentInformationTables</ParentRole>
      <Position>119</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R120.htm</HtmlFileName>
      <LongName>9955592 - Disclosure - Parent Company Only Financial Statements - Condensed - Schedule of Statements of Financial Condition (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ParentCompanyOnlyFinancialStatementsCondensedScheduleofStatementsofFinancialConditionDetails</Role>
      <ShortName>Parent Company Only Financial Statements - Condensed - Schedule of Statements of Financial Condition (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>120</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R121.htm</HtmlFileName>
      <LongName>9955593 - Disclosure - Parent Company Only Financial Statements - Condensed - Schedule of Statements of Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ParentCompanyOnlyFinancialStatementsCondensedScheduleofStatementsofIncomeDetails</Role>
      <ShortName>Parent Company Only Financial Statements - Condensed - Schedule of Statements of Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>121</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R122.htm</HtmlFileName>
      <LongName>9955594 - Disclosure - Parent Company Only Financial Statements - Condensed - Schedule of Statements of Cash Flows (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/ParentCompanyOnlyFinancialStatementsCondensedScheduleofStatementsofCashFlowsDetails</Role>
      <ShortName>Parent Company Only Financial Statements - Condensed - Schedule of Statements of Cash Flows (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>122</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R123.htm</HtmlFileName>
      <LongName>9955595 - Disclosure - Derivative Financial Instruments - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DerivativeFinancialInstrumentsNarrativeDetails</Role>
      <ShortName>Derivative Financial Instruments - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>123</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R124.htm</HtmlFileName>
      <LongName>9955596 - Disclosure - Derivative Financial Instruments - Schedule of Derivative Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DerivativeFinancialInstrumentsScheduleofDerivativeFinancialInstrumentsDetails</Role>
      <ShortName>Derivative Financial Instruments - Schedule of Derivative Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>124</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R125.htm</HtmlFileName>
      <LongName>9955597 - Disclosure - Derivative Financial Instruments - Schedule of Gain (Loss) on Derivative Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DerivativeFinancialInstrumentsScheduleofGainLossonDerivativeFinancialInstrumentsDetails</Role>
      <ShortName>Derivative Financial Instruments - Schedule of Gain (Loss) on Derivative Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>125</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R126.htm</HtmlFileName>
      <LongName>9955598 - Disclosure - Derivative Financial Instruments - Schedule of Key Characteristics of Interest Rate Derivative Transactions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DerivativeFinancialInstrumentsScheduleofKeyCharacteristicsofInterestRateDerivativeTransactionsDetails</Role>
      <ShortName>Derivative Financial Instruments - Schedule of Key Characteristics of Interest Rate Derivative Transactions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>126</Position>
    </Report>
    <Report instance="nwbi-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R127.htm</HtmlFileName>
      <LongName>9955599 - Disclosure - Derivative Financial Instruments - Offsetting Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.northwestsavingsbank.com/role/DerivativeFinancialInstrumentsOffsettingAssetsandLiabilitiesDetails</Role>
      <ShortName>Derivative Financial Instruments - Offsetting Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>127</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-K" isDefinitelyFs="true" isUsgaap="true" original="nwbi-20241231.htm">nwbi-20241231.htm</File>
    <File>nwbi-20241231.xsd</File>
    <File>nwbi-20241231_cal.xml</File>
    <File>nwbi-20241231_def.xml</File>
    <File>nwbi-20241231_lab.xml</File>
    <File>nwbi-20241231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles>
    <File>nwbi-20241231_g1.jpg</File>
    <File>nwbi-20241231_g10.jpg</File>
    <File>nwbi-20241231_g2.jpg</File>
    <File>nwbi-20241231_g3.jpg</File>
    <File>nwbi-20241231_g4.jpg</File>
    <File>nwbi-20241231_g5.jpg</File>
    <File>nwbi-20241231_g6.jpg</File>
    <File>nwbi-20241231_g7.jpg</File>
    <File>nwbi-20241231_g8.jpg</File>
    <File>nwbi-20241231_g9.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="3">http://fasb.org/srt/2024</BaseTaxonomy>
    <BaseTaxonomy items="3682">http://fasb.org/us-gaap/2024</BaseTaxonomy>
    <BaseTaxonomy items="15">http://xbrl.sec.gov/cyd/2024</BaseTaxonomy>
    <BaseTaxonomy items="39">http://xbrl.sec.gov/dei/2024</BaseTaxonomy>
    <BaseTaxonomy items="5">http://xbrl.sec.gov/ecd/2024</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
